Wednesday, September 02, 2009

New Mud Lobster on Semakau?

Update: Have dropped an email to the authors, Moh H. H. and Chong V. C., who wrote about the new species, Thalassina kelanang in RBZ. And they have confirmed that the mud lobster I found at Semakau is indeed Thalassina kelanang! Thanks to Prof. Chong Ving Ching and Moh Heng Heng for helping with the identification!

-------------

I could still remember after I saw a mud lobster on St John's Island, I told SY that it look somewhat different from the one that I have seen on Semakau, and I was wondering if they could be of different species. But then of course, there were only 2 species of mud lobsters, Thalassina anomala and Thalassina gracilis recorded in Singapore (Update: Apologies, there are currently 5 species of mud lobsters recorded in Singapore. The sources I was reading previously was outdated. Sorry for the mistake. Thanks Robin for the update. But guess this will not affect much my comparison below.), and since both mud lobsters I found were far too big to be Thalassina gracilis, I thought I was probably wrong.

However, recently, I read on The Raffles Bulletin on Zoology that a new species of mud lobster, Thalassina kelanang, was described from Malaysia, and I started to think if this new species can also be found in Singapore. Could either one of the mud lobsters I have found be the new species?

Mud Lobster
This is the mud lobster I found on Semakau on 11 April 2009 during a Project Semakau trip.

Mud Lobster
This is the mud lobster I found on St John's Island on 12 July 2009 during a field trip.

I decided to make a comparison between the mud lobsters I found and the description in the RBZ paper.

Mud Lobster
Mud Lobster
Taking a first look, it appeared that the Semakau mud lobster (on top) does look more similar to the new species, Thalassina kelanang, especially if you look at the shape of the backend of the carapace! The St John's mud lobster looks like a Thalassina anomala. But as the former was coated with mud at many places, it's not really clear enough for me to be sure.

I decided to take a closer look at the head of both mud lobsters.

Mud Lobster
Mud Lobster
On the head of both mud lobsters, there is this inverted V ridge with some kind of divider in the middle. For the case of Thalassina kelanang, the divider extends longer than the inverted V, just like the one on the Semakau mud lobster! For Thalassina anomala, the inverted V is longer, and this can be seen on the St John's mud lobster.

Next, I decided to look at the abdominal somite.

Mud Lobster
For Thalassina kelanang, it is more of an inverted Y shape (top left diagram, and Semakau mud lobster on top right), while for Thalassina anomala, the inverted Y is not as obvious (bottom left diagram, and St John's mud lobster on bottom right). Again, this is true for both mud lobsters!

Mud Lobster
Thalassina kelanang's pereopod 1 has a row of 8 to 12 strong dorsal spines (right arrow) on the inner propodal ridge, and the lateral dorsal ridge extends to three quarters or more of the propodal length (left arrow, see the little bumps end about four-fifth of the length). These are evident in the Semakau mud lobster shown above.

Mud Lobster
For Thalassina anomala, the pereopod 1 has a row of 13-20 blunt spines or tubercles on the inner propodal ridge (right arrow), and the lateral dorsal ridge extends the entire length of the propodus (left arrow, see the little obvious bumps extends all the way compare to the earlier photo).

From the photos above, it does seem that the Semakau mud lobster could be a Thalassina kelanang! Guess I will probably need to get a specimen the next time I see a mud lobster at Semakau, so that the experts can confirm the ID.

Guess I was rather lucky. I have seen mud lobsters twice on Semakau (didn't managed to take photo the second time), once on St John's, twice at Chek Jawa (only managed to take photo of part of one of them), and another time at Pulau Tioman.

Mud Lobster
The above is the mud lobster I found on Pulau Tioman. Doesn't quite look like the previous 2 species, as it has features that are similar to or different from either species. It is much smaller than the others that I have seen, so could it be a Thalassina gracilis? Or is it something new altogether? Hmm...

5 comments:

koksheng said...

Thks for taking so much effort to compare the species! Quite exciting to know the new species could be in Semakau.

Ivan said...

Indeed, it does raise a lot of interesting questions!

Hopefully we'll have more encounters and will be able to make such detailed comparisons like yours.

tHE tiDE cHAsER said...

Thanks both for your comments :)

Anonymous said...

Interesting find.

There is actually five mud lobster species in S'pore.

Check out http://rmbr.nus.edu.sg/rbz/biblio/s20/s20rbz121-158.pdf

Cheers
Robin

tHE tiDE cHAsER said...

Thanks Robin for the update. Guess I was looking at the outdated resources previously.